My ending with Halsin felt very different.
He told me to go into hiding and it wouldn't be a good idea to come with him because it would scare the children. I had to press him by saying he could change their minds and then I could come to visit and slowly introduce myself.
With Karlach it was different. She still loved me, but her ending was bad.
The more I read about the
endings, the more I see it as you
enthralling your love interest. Shadowheart's is similar, she thinks it's initially better to split up, then you "convince" (read: probably enthrall) her into accepting it, and allegedly this even happens for her Dark Justiciar ending where she normally leaves you. With the knowledge we have of the Emperor and Duke Stelmane, it's hard to ignore.
I'd guess it's the same for other companions.
